X.H.Modal: Cleanup
X.H.Modal: Cleanup

Mostly small things, like making imports line up with the provided
comments.  Also:

+ Rename mode' -> modeWithExit.  This seems like a better name for
  discoverability reasons.

+ Make the fields of Mode strict, because they have no reason not to,
  really.

xmonad/xmonad-contrib,xmonad/xmonad-contrib